Abstract

In Brazil, about 80% of the 60 million hectares of pasture are in some state of degradation. Among the causes of this degradation is the lack of investment in liming and fertilization at the time of planting. Phosphorus is especially critical because it stimulates root growth in the establishment phase of forage growth. The objective of the study was to evaluate different sources of phosphorus in the formation of Marandu and Xaraés forages. An experimental design of randomized blocks in a factorial arrangement, 2 x 4, with 5 repetitions was used. Treatments consisted of two cultivars of Urochloa brizantha: Marandu and Xaraés and three sources of phosphorus: triple superphosphate (41% P₂O₅), natural reactive phosphate (28% P₂O₅) and organic mineral (4- 14-8) plus the absence of phosphate fertilizer (control). Plant height, stem diameter, chlorophyll A and B content and fresh and dry matter mass were evaluated 60 days after germination. Leaf content was also examined for the following mineral nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn). The Marandu cultivar was superior to the Xaraés cultivar in terms of height. Among the sources of phosphorus examined, there were no significant differences among organic mineral, triple superphosphate and reactive phosphate, for any of the characteristics considered. All the sources, however, differed from the control. The maximum extraction of soil macronutrients by Urochloa brizantha was, in descending order: the macronutrients K>N>Ca>Mg>P>S and micronutrients Mn>Fe>Zn>Cu. These nutrients, thus, needed to be replaced as they were removed through grazing, to replenish the soil. The sources of phosphorus evaluated were not associated with differences in the leaf contents of Cu, Zn and S. The leaf content of the Xaraés cultivar had higher values of N, P, K, Ca, Mg, S, Mn and Zn in relation to Marandu.

Key words: Forage, degraded area, mineral nutrients, fertilization.